The corrosion of metal surfaces is of obvious economic significance in many industrial applications and, as a consequence, the inhibition of corrosion is a matter of prime consideration. It is of particular significance to users of steel and other ferrous alloys. The corrosion of such ferrous metal alloys is largely a matter of rust formation which in turn involves the overall conversion of the free metal to its oxides.
The theory which best explains such oxidation of ferrous metal articles postulates the essential presence of both water and oxygen. Even minute traces of moisture are sufficient, according to this theory, to induce dissolution of the iron therein and the formation of ferrous oxide until the water becomes saturated with ferrous ions. The presence of oxygen causes oxidation of the resulting ferric hydroxide which settles out of solution and is ultimately converted to ferric oxide or rust.
The above sequence of reactions can be prevented or at least to a large measure inhibited, by relative impermeable coatings or films which have the effect of excluding moisture and/or oxygen from contact with the metal surface. Such coatings are often exposed to high humidity, corrosive atmosphere, etc., and to the extent that these coatings or films are penetrated or otherwise harmed by such influences they become ineffective for the desired purpose. It is also important that such coatings adhere tightly to the metal surface and resist flaking, crazing, blistering, powdering and other forms of loss of adhesion. A satisfactory corrosion-proofing coating or film then, must have the ability to resist weathering, high humidity, and corrosive atmospheres such as salt-laden mist or fogs, air contaminated with industrial wastes, road dirt, calcium chloride, etc., so that the protective coating or film is maintained on most, if not all, of the metal surface.
The corrosion of metal surfaces is of particular economic concern to owners and manufacturers of automotive vehicles. For instance, every car owner is aware of the corrosion which begins on the inner or underside of automobile bodies such as inside rocker panels, fender wells, headlight assemblies and door panels. The corrosive rate is especially high in certain geographic areas which are subjected to severe weather during the winter months necessitating the use of sand, salt, calcium chloride, cinders, etc., to maintain roads in usable condition. Under these conditions, it generally is only a matter of time before the relatively light gauge automotive body steel is completely converted to ferric oxide or rust. When this point is reached, the high quality exterior finishes flake off and reveal the metal destruction which has occurred to the body of the vehicle.
Automotive manufacturers have waged a constant battle against such body corrosion. Mastics and sealers have been used extensively as physical barriers to corrosive agents, and corrosion inhibiting primers have been used on underbody surfaces when they do not interfere with production line welding operations. When possible, zinc coated galvanized steel is used in substantial amounts to produce many body components directly exposed to corrosive agents. These efforts and many others, however, have only reduced underbody corrosion problems; the problem remains. The asphaltic mastic undercoatings failed to give the desired permanent protection against corrosion since on hardening due to age, these coatings would crack and lose adhesion, especially when exposed to low ambient temperatures.
Corrosion inhibiting paints have also been utilized as underbody coatings, but these are not particularly desirable because of the degree of metal preparation required prior to their application.
It is, therefore, an object of this invention to provide novel rust inhibitive water dispersed coating compositions for the protection of metals.
It is also the object of this invention to provide novel rust-inhibitive coating compositions which compositions may be easily and inexpensively applied to metal surfaces.
It is also the object of this invention to provide novel rust inhibitive coating compositions which can be applied to such metal surfaces in the form of water dispersed coating compositions.
These and other objects of the invention will become apparent from a reading of this specification.